With the development of technology for computing, various types of devices offering personalized information have been developed. For example, computational research and the development of clothes which people normally wear, or various research activities, in which attempts have been made to insert a computational function into a variety of accessories, such as hats or bags, which people use in daily life or into daily necessities such as curtains that are made of fiber or textile, have been noticeably being undertaken.
As a variety of computers have been developed, communication with external devices is actually regarded as an important factor in the development of various applications. A wearable computer, which is representative of computational systems made of textiles, is important for communicating with various devices offering personalized information and peripheral devices located therearound. A requirement of such a wearable computer is that it not be harmful to a communication interface, particularly a human body that is well harmonized with the textile.
Representative short-range communication methods include local area networks, Bluetooth which belongs to a WPAN (Wireless Personal Area Network), ZigBee, and the like. As for these existing methods, methods such as Bluetooth and an electromagnetic inductive coupling method which use electromagnetic waves lack countermeasures in terms of security and against the electromagnetic waves which exert an influence on the human body.
Further, free-space communication has the advantage of low power consumption when performing communication, and uses an infrared data association (IrDA) using infrared light or uses visible light communication (VLC) using visible light. A restriction placed on free-space communication is that communication can be maintained only when a line of sight (LoS) is ensured in view of the characteristics of optical communication.
There has been a lot of previous research into optical communication that is not harmful to the human body for the purpose of providing information exchange between information devices such as mobile phones. The optical communication uses infrared light or visible light and has the advantage of low power consumption when performing communication.
There is the restriction that, to ensure a LoS because of the characteristics of optical communication, a light emitter and a receiver of a photodetector need to be located within a certain distance and angular range within which they can communicate with each other.
Thus, a user experiences difficulty in that the user needs to manually place the information devices at the correct position to perform information exchange using conventional optical communication.